Parenteral administration (intravenous, intramuscular and subcutaneous) of biologically active agents, such as drugs, is normally regarded as the most effective route of administration. However, administration by injection has a number of disadvantages. Injection of a biologically active agent requires the use of sterile syringes and administration by trained personnel, and may cause pain and irritation, particularly in the case of repeated injections. This route of administration poses a risk of infection. More significantly, intramuscular injections are often poorly tolerated by the individual, and may possibly cause an induration (hardening of tissue), haemorrhage (bleeding) and/or necrosis (local death of tissue) at the injection site.
The mucosal membrane is connected to an extensive network of blood capillaries under the nasal mucosa, which makes the membrane highly suitable for drug delivery (delivery of biologically active agents), particularly suited to provide rapid absorption of biologically active agents, providing a rapid pharmacological response. One example of such a mucosal membrane is the nasal epithelial membrane, which consists essentially of a single layer of epithelial cells (pseudostratified epithelium), the mucosal membrane is therefore very suitable for drug delivery.
A variety of vehicle systems for intranasal drug delivery have been developed. One of the problems encountered in using such vehicle systems, is the local irritation and lack of rapid absorption. Without the rapid rate of absorption, the biologically active agents, such as drug substances, may be cleared from the absorption site before they are absorbed into the systemic circulation, into the lymphatic system or into the brain, whichever is relevant.